What causes successive runs of nested function to be slower?

I'm running into a problem that is outside of my experience with MATLAB. I have a function that has repeated calls to a nested function. Each run of the nested function takes longer than the first, in an alternating pattern of approximately 15 seconds longer, then 100 seconds longer (listed below).

I cannot post the full function at this time, but here are some relevant parts.

• Parent function defines all input variables for nested function.
• runFactors (array) is passed to nested function as input argument, all other variables used are from within parent function
• Output is a pair of arrays
• No variables are cleared during the function run (only overwritten)
• Sub function does simple addition/multiplication of multiple configurations from multiple input arrays (e.g. A(1) + B(1) + C(1), A(2) + B(1) + C(1), A(2) + B(2) + C(1), etc.) and reports the maximum.
• Size of arrays does not change between function calls.
• The same input data (arrays) is used for each run of the nested function.

The section from the parent function calling the nested function:

    %Running stress calculations
    waitbar(0,h,'Calculating Stresses...');
    time0 = toc
    [stressFull,mpFull] = calcStressesBend(runFactors(1,:));
    time1 = toc - time0
    [stressLessPres,~] = calcStressesBend(runFactors(2,:));
    time2 = toc - time1
    [stressLessUllage,~] = calcStressesBend(runFactors(3,:));
    time3 = toc - time2
    [stressLessAero,~] = calcStressesBend(runFactors(4,:));
    time4 = toc - time3
    [stressLessTherm,~] = calcStressesBend(runFactors(5,:));
    time5 = toc - time4
    [stressLessED,~] = calcStressesBend(runFactors(6,:));
    time6 = toc - time5
    [stressIntOnly,~] = calcStressesBend(runFactors(7,:));
    time7 = toc - time6
    [stressThermOnly,~] = calcStressesBend(runFactors(8,:));
    time8 = toc - time7
    [stressEDOnly,~] = calcStressesBend(runFactors(9,:));
    time9 = toc - time8
    [stressAeroOnly,~] = calcStressesBend(runFactors(10,:));
    time10 = toc - time9
    [stressUllOnly,~] = calcStressesBend(runFactors(11,:));
    time11 = toc - time10
    [stressPresOnly,~] = calcStressesBend(runFactors(12,:));
    time12 = toc - time11

Runtime results:

• time1 = 119.30 s
• time2 = 134.89 s (15.6 s longer)
• time3 = 238.45 s (103.6 s longer)
• time4 = 252.17 s (16.7 s longer)
• time5 = 356.10 s (103.9 s longer)
• time6 = 370.89 s (14.8 s longer)
• time7 = 474.17 s (103.3 s longer)
• time8 = 488.28 s (14.1 s longer)
• time9 = 591.66 s (103.4 s longer)
• time10 = 605.60 s (13.9 s longer)
• time11 = 709.23 s (103.6 s longer)
• time12 = 722.91 s (13.7 s longer)

Is there something causing each call to create a copy of the variables in the parent function? Is there some simple change to prevent this (persistent, etc)?

Thanks for your help, Joel